Res judicata is the generic term for a group of related concepts concerning the conclusive effects given final judgments. Within this general doctrine there are two principal categories: (1) claim preclusion—also known as res judicata; and (2) issue preclusion—also known as collateral estoppel.

These legal doctrines generally preclude litigants from relitigating claims and issues that were previously litigated to a final resolution or judgment.

In Missouri, res judicata, or claim preclusion, prevents a party from relitigating a claim that has already been finally adjudicated in a previous lawsuit. This doctrine applies when the earlier lawsuit resulted in a final judgment on the merits, involved the same parties or their privies, and was based on the same claims or causes of action. Issue preclusion, also known as collateral estoppel, bars the relitigation of factual or legal issues that were actually litigated and determined by a valid and final judgment in a prior action, even if the second lawsuit differs in terms of claims or causes of action. The party against whom the doctrine is invoked must have been a party to the original action, or in privity with such a party, and the issue must have been essential to the judgment. These doctrines are grounded in the interest of judicial economy, preventing unnecessary litigation, and upholding the finality and integrity of court judgments. Both state statutes and case law in Missouri govern the application of res judicata and collateral estoppel.